Lab 4: Determining temperature from a temperature sensor

Transcription

1 Start on a fresh page and write your name and your partners names on the top right corner of the page. Write the title of the lab clearly. You may copy the objectives, introduction, equipment, safety and procedure sections, or you may print this handout and neatly tape in these sections into the appropriate pages in your lab notebook. Preserve the habit of using only the right-hand page. Note that there are three sections you need to prepare: Write the circuit diagram section based on the write-up Look up the manufacturer data sheet for the temperature sensor you are using, and derive the formula for determining temperature from measured voltage Write Arduino code to obtain temperature data from the sensor Set up a data table in the data section, which will compare a measured temperature with the reported temperature from the sensor The writeup to this lab is due 4 p.m., Friday, February 16, in my mailbox, though you may submit it earlier in class. The writeup consists of a photocopy of your lab notebook pages for Lab 4, from the title page to the conclusion section. Physics 222 Objectives: Lab 4: Determining temperature from a temperature sensor Building a circuit with a low-voltage analog sensor, calibrating and testing it Writing code to run the sensor, including input and output onto an SD card Fine-tuning the sensor to give more accurate readings Introduction and relevant formula: The Analog Devices TMP36 Temperature Sensor is used to measure the ambient temperature. However, what the device actually outputs is a voltage. Fortunately, the output voltage is proportional to the temperature, so it s a matter of calibrating the voltage to conform with the temperature. Open the data sheet from the manufacturer, Analog Devices; fortunately, the University of Michigan Engineering Program has already scanned that in for you: The sensor is shown in Figure 4. T-3 (TO-92). Quoting from the data sheet: The TMP36 is specified from 40 C to +125 C, provides a 750 mv output at 25 C, and operates to 125 C from a single 2.7 V supply Both the TMP35 andtmp36 have an output scale factor of 10 mv/ C. From this information, derive the linear formula for the temperature sensor (e.g., y = mx + b form).

2 Remember that the analog inputs of the Arduino convert a voltage input between 0 and 5 V into a number between 0 and Write the Arduino code (or pseudo-code) that receives input from the TMP36 sensor and outputs the Celsius temperature to the serial monitor using the formula you determined above. Some tips: One particular line that will be helpful is Serial.println(temp_C); which will cause a line space to appear between data entries. The analogread command receives input from the sensor and converts it into a variable (note the variable declaration that precedes it!): float voltage = analogread(pintemp); Add a 1 second delay between readings and limit the number of readings, unless you want to be overwhelmed by data and are unable to turn off the readings except by terminating the power. Finally, one drawback with the Arduino system is that there is no command to write data to a.txt or other common file format. There are third-party software that will mimic the serial monitor that do have the ability to write to other formats; you will test one of those. Equipment Analog Devices TMP36 Temperature Sensor Arduino kit (including SD card reader shield) and laptop Various known temperature items: (list what you use here) Circuit diagrams There are resistors within the TMP36 Device, so no external resistance is needed. Show the connections between the Arduino Board and the TMP36 sensor, based on the design of the TMP36 sensor and step 2 of the procedure. This means drawing pin-to-pin lines (the sensor and the Arduino may be represented as squares, with labeled pins on each).

3 Safety Both the Arduino Board and the TMP36 sensor are easily damaged by static electricity. Furthermore, if the TMP36 sensor is incorrectly wired, it will grow UNTOUCHABLY HOT QUICKLY. If this occurs, do not remove the sensor simply cut the power to the board. Procedure (Work in teams of two; one person does the a steps, the other the b ) Part A (Making a functional temperature sensor) 1a. Set up the circuit drawn in the Circuit Diagram section on the breadboard. 1b. Obtain a laptop, power it up, and open the Arduino software (there should be an icon on the desktop). 2a. Connect pin 1 to 5 V on your Arduino, the middle pin (Out) to A0 or some other analog input pin on your Arduino, and pin 3 to 0 V (GND). 2b. Enter the code developed in the Relevant equations section. Compile and export to the Arduino (make sure the proper COM port is selected under Tools ). Obtain some temperature data. 3a. Calibrate the temperature from the sensor with the temperature measured with other devices; do this for several different temperatures, and record these temperature data in the data section. List both the new device(s) used and the different temperature materials in the equipment section. 3b. Modify the code to obtain more accurate temperatures from the sensor; note that this may alter the information given by the manufacturer on the data sheet. Part B (Exporting obtained sensor data) 4b. Plug the SD card reader shield onto the Arduino. The SD card shield has the same digital, analog, 5V and GND pins that the microcontroller board has. Plug the SD shield into the Arduino, being careful to line up the pins from the shield and the holes on your board. Then connect the three wires from the temperature sensor to the SD shield in the appropriate spots. Your sensor should work as it did before (you should check the Serial Monitor to see the temperature readings).

4 An alternative: Obtain alternate serial monitor software by going to and scroll down and download the CoolTerm application to your Desktop and then unzip the files. There is no Installer, so this should work just fine on any school laptop. Open CoolTerm.exe (hint: some of the laptops already have this software on their Desktops). 5b. Insert the SD card into the reader. To write temperature data to the SD card, modify your program by inserting your program into the program below. Note that if you named your variables differently you will have to modify the program accordingly. // SPI and SD libraries. SPI for connecting SD card to SPI bus. #include <SPI.h> #include <SD.h> const int sdpin = 4; // Temperature sensor middle pin set to analog 0 const int tempin = 0; // Delay time. How often to take a temperature reading, in miliseconds const int delaytime = 1000; // File variable File tempsfile; void setup() { // Serial output for when connected to computer Serial.begin(9600); while (!Serial) { ; // wait for serial port to connect. Needed for native USB port only Serial.print("Initializing SD card..."); if(!sd.begin(sdpin)) { Serial.println("initialization failed!"); return; Serial.println("Initialization done."); void loop() { // Open SD card for writing tempsfile = SD.open("tempC.txt", FILE_WRITE); if (tempsfile) { // Your code that reads the sensor and calculates tempc goes here //Note that analog pin 0 is called tempin (insert your code here) // write temps to Serial Serial.println(tempC);

5 // write tempc to SD card tempsfile.println(tempc); // close the file tempsfile.close(); else { Serial.println("Error opening file in loop."); delay(delaytime); Send this program to the Arduino board and open the serial monitor. You should see your temperature data as before (use the various temperature objects to make sure it held calibration). 6b. Check to see if the file is there: go to Files Examples SD, and open and send the program listfiles to the Arduino. (Note: There are other example programs including one called Files which lets you delete a file on the SD card). Open the Serial Monitor and it should show that you have a tempc.txt file on the SD card. Remove the SD card and plug it into the appropriate port in the classroom laptops. Open the tempc.txt file onto the graphing program of your choice and print out the graph of time versus temperature. Give the graph an appropriate title, axes labels and units (no linear regression necessary). Part C (Using the temperature sensor as a trigger) 7a. Modify the circuit so an LED is wired into circuit parallel to the temperature sensor (that is, the LED is not in series with the sensor; in fact, it should be deriving its power from one of the digital power pins like 9 or 13). 7b. Modify the Arduino code so that the LED lights up if the sensor temperature is more than 25 C. For an added challenge, make the LED light up if the sensor temperature is more than 2 C higher than the temperature the sensor had been recording for the past ten seconds. 8. Write a separate circuit diagram that shows the modified circuit, and write (or print and paste a copy of) the modified code, with plenty of in-code documentation (i.e., comments about what each line does). Data and analysis Part A Temperature measured by the sensor: C Temperature measured by : C

6 (at least three pairs of measurements) Final copy of code used Part B Time/temperature graph (see procedure) Part C Circuit diagram modified to include LED branch Modified code showing temperature trigger Discussion and conclusion Did the temperature sensor give reliable readings? Which may be broken down into: Did the sensor, in fact, work at all? How noisy were the temperature readings (in other words, estimate the uncertainty in temperature from the sensor)? How did this compare to what the manufacturer claimed on their data sheet? Was there an optimal delay? Why was this value optimal? Give an estimate of the time each individual part took (including how much time each person spent on their part), and explain why certain sections were particularly time-consuming, with an eye to helping the next group of students achieving success in less time.